WASHINGTON — Democrats' first impeachment hearing quickly turned hostile Tuesday as their sole witness, former Trump campaign manager Corey Lewandowski, stonewalled many of their questions and said they were "focusing on petty and personal politics."

Lewandowski, a devoted friend and supporter of President Donald Trump, was following White House orders not to discuss conversations with the president beyond what was already public in former special counsel Robert Mueller's report. Trump was cheering him along as he testified, tweeting that his opening statement was "beautiful."

The hearing underscores what has been a central dilemma for House Democrats all year as they try to investigate — and potentially impeach — Trump. Many of the Democrats' base supporters want them to move quickly to try to remove Trump from office. But the White House has blocked their oversight requests at most every turn, declining to provide new documents or allow former aides to testify.

On Tuesday, Lewandowski made clear he wouldn't make life easy for the Democrats. He demanded that Democrats provide him a copy of the Mueller report, sending Democratic staff scrambling to find one. He then read directly from report, showing that he wouldn't say much beyond what Mueller wrote. Republicans on the panel then forced a series of procedural votes, immediately sending the hearing into disarray.

"He's filibustering," a frustrated Nadler said.

Lewandowski eventually began to answer some questions — he told the committee that he doesn't think "the president asked me to do anything illegal" — but still stuck mostly to what was already in the report, giving Democrats little new information to go on. And he made clear his dislike for the House majority in the opening statement, calling them petty and asserting that investigations of the president were conducted by "Trump haters."

Democrats say the blockade from the White House and stonewalling from witnesses like Lewandowski just give them more fodder for lawsuits they have filed against the administration — and possible articles of impeachment on obstruction.

Two other witnesses who were subpoenaed alongside Lewandowski, former White House aides Rick Dearborn and Rob Porter, did not show up at all, on orders from the White House.

"This is a cover-up plain and simple," Nadler said, of the White House orders. "If it were to prevail — especially while the Judiciary Committee is considering whether to recommend articles of impeachment — it would upend the separation of powers as envisioned by our founders."

The Republican Senate is certain to rebuff any House efforts to bring charges against the president. And moderate Democrats in their own caucus have expressed nervousness that the impeachment push could crowd out their other accomplishments.

Still, the Judiciary panel is moving ahead, approving rules for impeachment hearings last week. Among those guidelines is allowing staff to question witnesses, as will happen for the first time with Lewandowski.

Tuesday's hearing alternated between combative exchanges between Lewandowski and Democrats and friendly questions from the Republican side of the dais.

"They are going to bring back anybody, as much as they have to, to find something, anything to keep impeachment hopes alive," Rep. John Ratcliffe, R-Texas, told Lewandowski during his round of questioning.

Lewandowski was a central figure in Mueller's report, which the committee is examining as part of its impeachment probe. Mueller's investigators detailed two episodes in which Trump asked Lewandowski to direct then-Attorney General Jeff Sessions to limit Mueller's investigation. Trump said that if Sessions would not meet with Lewandowski, then Lewandowski should tell Sessions he was fired.

Credit: RYAN MCBRIDE/AFP/Getty Images

Corey Lewandowski, October 28, 2016 in Manchester, New Hampshire.

Lewandowski never delivered the message but asked Dearborn, a former Sessions aide, to do it. Dearborn said he was uncomfortable with the request and declined to deliver it, according to the report.

Under questioning by Rep. Hank Johnson, D-Ga., Lewandowski confirmed as "accurate" that Trump had asked him to deliver the message. At least two Democrats asked if he "chickened out." Lewandowski said no — he took his kids to the beach instead.

The hearing could be considered an audition of sorts for Lewandowski, who is considering a run for Senate in New Hampshire next year. In the hours before the hearing, he tweeted that his followers should "tune in" to the hearing and used the hashtag "2020."

The White House issued its orders to Lewandowski in letters released late Monday. White House counsel Pat Cipollone wrote that Lewandowski, who never worked in the White House, should not reveal private conversations with Trump beyond what is in Mueller's report. He wrote that his conversations with Trump "are protected from disclosure by long-settled principles protecting executive branch confidentiality interests."

Cipollone also said that Dearborn and Porter were "absolutely immune" from testifying. He said the Justice Department had advised, and Trump had directed, them not to attend "because of the constitutional immunity that protects senior advisers to the president from compelled congressional testimony."

Porter, a former staff secretary in the White House, took frequent notes during his time there that were detailed throughout the report. He resigned last year after public allegations of domestic violence by his two ex-wives.

Democrats say the White House's rationale isn't legally sound and are challenging the idea of "absolute immunity" in court.